Normally if you want to block all requests to and from an IP address, iptables is an ideal solution. A rule similar to this one would be handy
/sbin/iptables -A INPUT -s 1.2.3.4 -j DROP
What if you want to block that IP without using iptables, route command would do the job
/sbin/route add -host 1.2.3.4 reject
